A secondary battery such as a lithium ion secondary battery has an electrode plate group formed by alternately superposing positive electrode plates and negative electrode plates on each other such that separators are interposed between the positive and negative electrode plates. Available as one of devices for manufacturing the electrode plate group is a zigzag stack type manufacturing device which folds a continuous body of a separator in a zigzag fashion, inserts the positive electrode plates and the negative electrode plates into its respective folds, and squashes the resulting combination flat (see, for example, Patent Document 1). With such a zigzag stack type manufacturing device, the continuous separator is held between a pair of rollers, the paired rollers are moved in a reciprocating manner in a horizontal direction to fold the separator zigzag and, upon each reciprocation of the pair of rollers, the positive and negative electrode plates are placed on the separator alternately.
In an attempt to shorten the tact time further using the zigzag stack type manufacturing device of Patent Document 1, the present inventors proposed a manufacturing method and a manufacturing apparatus for a secondary battery capable of improving the position accuracies of positive and negative electrodes and a separator (see Patent Document 2). According to the manufacturing method and apparatus, a belt-shaped separator is suspended from above in a tension-free state, and a plurality of guide members are crossed horizontally between their rows to fold the separator (or a superposed body comprising one of a positive electrode plate and a negative electrode plate sandwiched between two separators) in a zigzag manner. Positive electrode plates and negative electrode plates (in the case of the superposed body, the electrode plates other than the sandwiched one electrode plate) are inserted into the resulting folds to produce an electrode plate group of a secondary battery in which the positive electrode plates and the negative electrode plates are superposed in layers, with the separator being sandwiched between them. The separator has an upper side accommodated within an accommodation case disposed above a zigzag folding means, whereby the separator is suspended downward via a roller, and a lower side of the separator is accommodated within a similar accommodation case disposed below the zigzag folding means. In this manner, the upper side and the lower side of the separator are accommodated in the upper and lower accommodation cases, so that a buffer part (excess length part) in zigzag folding the separator is secured. That is, during zigzag folding, the right and left guide members move in directions, in which they approach each other, to pull in the separator in the same direction. A separator length for allowing the separator to follow this motion needs to be secured.